Rotary pumps comprise a rotatable feed wheel and, for adjusting their specific delivery volume, an actuating member which surrounds the feed wheel and can be moved back and forth and to which a control fluid is applied in one direction of its mobility and a restoring force is applied counter to the control fluid force exerted by the control fluid. The pressure of the control fluid is dependent on the pressure of the fluid delivered by the pump. In most applications, a portion of the fluid delivered by the pump is diverted and fed to the actuating member as the control fluid. In order to seal a control pressure space to which the control fluid is applied, the actuating member forms a radial sealing gap at its circumference in sliding contact with a co-operating surface, and a sealing gap at each of its axial facing sides. Due to differences in the thermal expansion of the components forming the sealing gaps, the widths of the sealing gaps change as a function of the temperature of the pump. In most pump embodiments, the sealing gaps increase in size as the temperature increases. The sealing gaps can also increase in size due to wear, in particular during running-in. Production tolerances are another cause of inaccuracies with regard to the delivery volume. If the pump is regulated down by means of the control fluid, i.e. the control fluid is applied to the actuating member in the direction of reducing the specific delivery volume, then the pressure level at which the pump begins to be regulated down shifts with temperature and, over time, wear. Production tolerances are responsible for differences from pump to pump.
Pumps such as the invention relates to inter alia are known for example from WO 2006/066405 A1, WO 2007/128105 A1 and WO 2010/142611 A1, which are incorporated by reference. Sealing elements which are arranged in the circumferential sealing gaps are used to improve the seal.